I have been a bit reluctant to answer your question hoping that someone from your part of the world would respond. Never mind - here's a UK point of view. I have always understood that what kills Sempervivums in the winter isn't the cold. What they can't cope with is cold combined with wet. Your plants will do well I think if they are left outside with a bit of protection to prevent them from getting wet. Giving Semps. the houseplant treatment will turn them into softies and they will lose their beautiful colours. These are plants of the mountains so they are pretty tough on the whole. I'm just hoping that you don't report back next year that all your plants have been killed off.

i live not far from buffalo and im sure you know our winters are cold and snowy. i planted some sempervivum last summer and we had a brutal cold winter with a good amount of snow. they were fine come spring. they are in a raised bed and there is mulch in the bed, but i did not cover them.

My experience with my semps in the very cold and very hot mountains is that below zero temps and snow never killed a one! They bounce right back - but don't mulch: that will collect water around the plants and give them a crown rot. Just make sure that they have EXCELLENT drainage and don't get waterlogged. Sempervivums seem to need a cold dormant period in order to take off again & color up in the Spring - but my friend has been successfully keeping her little S. Tectorum colony on her SUNNY kitchen windowsill year-round for a couple of years.

No, do NOT mulch sempervivum for the winter. The excess moisture that is held in the mulch will kill the plants. They are perfectly cold hardy here in MN. Just plant them in well-drained soil and full to almost full sun. You shouldn't have any problems.

I grew S. 'Oddity' for a number of years under fluorescent lights (4" below the tubes) before I knew that it was completely winter hardy. As long as you can give the plants the amount of light that they will want, you shouldn't have any problem. If the plants are special to you, and you have a clump of them, I would separate a couple of the plants and put them outside so you are sure that you will have them again next year.
Good luck,
Mike

Thank you all very much. You have unwittingly given me the nerve to try sempervivums here in Texas. I was worried about them surviving our winter but if you have them outside in Minnesota then it looks like it will be a good investment here. I do drool over them everytime i see them but stop myself because i didn't know what to do with them in the winter. We never stay cold here long but we do drop below 20 degrees at least a few times over the winter. Thanks again and if you have any more advice for me trying to do them in Texas please shower me with your wisdom! lol

'Sunrisefairy', as long as you have them in a sunny location with good drainage, they should over-winter for you. Our winters here in south carolina tend to be very wet, and this past winter we had many nights of temperatures in the teens w/ freezing rains. My semps. did fine, as did all of my sedums.

Sempervivum do fine in zone 3 in exposed raised alpine troughs...so they will do fine in Minnesota.

As stated above, the enemy is 'wet cold'. As long as temperatures are below zero then a covering doesn't hurt but best to remove leaves early in the season (mid March in zone 3).